Effect of Sample Introduction on ICP-MS Detection of Nonmetal Analytes in a Simulated HPLC Matrix

1. 1. Experimental Setup Effect of Sample Introduction on ICP-MS Detection of Nonmetal Analytes in a Simulated HPLC Matrix Adam E. Dill and Jon W. Carnahan Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL, 60115 Overview • With the increase in heteroatom moieties (P, S, Cl, F, for example) in pharmaceutical compounds and impurities, the detection and quantification of nonmetals has become increasingly important to the pharmaceutical industry. • Demand for heteroatom detection in the pharmaceutical industry is a function of the high sensitivity and genotoxic impurity requirements for the manufacturing of pharmaceutical compounds. • An argon inductively coupled plasma (ICP) is a versatile, robust, and nearly structurally independent source for trace elemental analysis that can be applied to the detection of heteroatom moieties in pharmaceutical compounds. • Solutions containing the active pharmaceutical ingredient phosphomycin in one of three buffers common LC buffers; ammonium acetate, ammonium hydroxide, and formic acid; are used to monitor phosphorus. • Operational parameters of several nebulizers are varied to determine which nebulizers may be useful for coupling ICP-MS to LC separations. • One general comment – You have a great set of results – it would be nice if the results in terms of trends related to nebulizer characteristics…… this is important info !!! 7. Results for HEN170A • The experimental setup for all experiments is diagramed below: • ICP-MS operating parameters are listed below in Table 1: 3. Results for U5000AT 4. U5000AT Discussion 8. HEN170A Discussion • See section 14 for a graphical representation of the data • See section 12 for a graphical representation of the data • Best detection occurs at higher values of Qg and Ql • Can easily nebulize entire range of Ql values tested • Droplets formed such that residence time affects overall detection limit at most by one order of magnitude • Large range of Qg and Ql (l subscript- also sec 6) work well for optimal detection with this nebulizer • RSD% of all signals higher than other nebulizers: • May be poor for maintaining peak shape post UV detection • See table comparing signal RSD% of all nebulizers in section 11 • Performance profile (surface plot) seen in section 12 is similar in shape to other high efficiency nebulizers such as HEN90A and HEN170A: • Likely a result of similar droplet size and size distribution • Performance makes nebulizer attractive for coupling to HPLC: • Although high signal RSD% may pose a problem • Best detection occurs at higher values of Qg and Ql • Can easily nebulize entire range of Ql values tested • Droplets formed such that residence time affects overall detection limit at most by a factor of 3 • Large range of Qg and Ql work well for optimal detection with this nebulizer • RSD% of all signals lower than USN or C30: • May be good for maintaining peak shape post UV detection • See table comparing signal RSD% of all nebulizers in section 11 • Performance profile (surface plot) seen in section 12 is similar in shape to other high efficiency nebulizers such as HEN90A and USN: • Likely a result of similar droplet size and size distribution • Performance makes nebulizer attractive for coupling to HPLC • Performance equivalent or better than C30 with ~10X less sample 2. Methods and Materials • Methods: • Phosphorus containing solutions were continuously nebulized and phosphorus was monitored at m/z=31 • All solutions contained 250 ppb P in the form of phosphomycin • All solutions were 80:20 (v/v%) methanol:water and contained one of three buffers: • 0.1% (v/v%) Ammonium Hydroxide • 10 mM Ammonium Acetate • 0.1% (v/v%) Formic Acid • Ql (liquid sample flow rate) varied by calibrated peristaltic pump • Qg(nebulizer gas flow rate) varied by Ar(g) calibrated mass flow controller • For each nebulizer and solution, maximum phosphorus signal was obtained by optimizing: • Torch position • Qg • Ql • Once maximum phosphorus signal was obtained, various Qg and Ql values were (spacing issues on orig) tested • Materials: • HPLC grade methanol (Fischer) • 28(?)% (w/w%) Certified ACS plus ammonium hydroxide (Sigma-Aldrich) • 96% (wt/wt%) ACS reagent formic acid (Sigma-Aldrich) • Reagent grade ammonium acetate (Sigma-Aldrich) • Phosphomycin calcium salt (Sigma-Aldrich) • Instrumentation used in these experiments included: • Fisons (Thermo Electron) Instruments PlasmaQuad II ICP-MS: • Nebulizers: • Cetac U5000AT Ultra Sonic Nebulizer • Meinhard HEN170A • Meinhard HEN90A • Meinhard TR30-C1 • Membrane Desolvation: • Cetac MDX-200 • Scott-Type Dual Pass Spray Chamber • Rainin Rabbit Peristaltic Pump • Brooks 5890 Mass flow Controller 5. Results for TR30-C1 9. Results for HEN90A 6. TR30-C1 Discussion 10. HEN90A Discussion • See section 13 for a graphical representation of the data • See section 15 for a graphical representation of the data • Best detection occurs at higher values of Qg and Ql • Can easily nebulize entire range of Ql values tested • Droplets formed such that residence time affects overall detection limit at most by a factor of 3 • Large range of Qg and Ql work well for optimal detection with this nebulizer • RSD% of all signals lower than USN or C30: • May be good for maintaining peak shape post UV detection • See table comparing signal RSD% of all nebulizers in section 11 • Performance profile (surface plot) seen in section 12 is similar in shape to other high efficiency nebulizers such as HEN170A and USN: • Likely a result of similar droplet size and size distribution • Performance makes nebulizer attractive for coupling to HPLC • Performance equivalent or better than C30 with ~10X less sample • Best detection occurs at moderate and lower values of Qg and Ql • Efficiently nebulizes with only a small range of Ql values tested: • At lower Ql there is an increase in the ration of gas kinetic energy to liquid mass ratio • Droplets formed such that residence time affects overall detection limit by at most by a factor of 3 • RSD% of all signals higher than HEN style nebulizers but lower than USN: • Likely less problematic than USN for maintaining peak shape post UV detection • See table comparing signal RSD% of all nebulizers in section 11 • Performance profile (surface plot), seen in section 13, maximum generally occurs at different position from HEN and USN style nebulizers: • A result of different efficiency, droplet size, and droplet size distribution • Performance makes nebulizer possible but not as attractive as other nebulizers for coupling to HPLC Acknowledgements We gratefully acknowledge the NIU Department of Chemistry and Biochemistry and NIU Graduate School. Special thanks to members of NIU technical staff. (Meinhard and Ion Flight)